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77th EAGE Conference and Exhibition 2015
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
1 - 50 of 980 results
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Total-variation Based Seismic Imaging with Bregmanized Operator Splitting Algorithm
Authors T. Zand, A. Gholami and M.D. SacchiThe Born approximation of wave equation provides the possibility of determining the Earth velocity model from pre-stack seismic data. But ill-conditioning of the linearized problem is a major challenge. In this paper, in order to solve the problem and find an appropriate velocity model the total variation (TV) regularization is used to force the velocity model to have sparse gradient. Such a constraint allows selecting a model that has sharp boundaries between adjacent layers. We employ the Bregmanized Operator Splitting (BOS) algorithm to solve the problem. Numerical examples show high performance of the proposed method for velocity model building.
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Verification of Bright Spots Using Fluid Factor Attribute in Miocene Deposits of the Carpathian Foredeep (SE Poland)
Authors K. Cichostepski and M. KasperskaThe Miocene deposits of the Carpathian Foredeep are known for its lithological variability and uneven compaction. These circumstances often cause occurrence of many bright spots which are not connected with gas accumulations. Standard seismic reservoir interpretation using only post-stack attributes can lead to wrong conclusions in such area. That is why it is very important to find a valid method for verification of these bright spots. In this paper we propose the Fluid Factor attribute for validation of bright spot anomalies in the Miocene deposits of the Carpathian Foredeep. The application of pre-stack attributes significantly reduced ambiguity of reservoir interpretation.
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Geochemical Characteristics of Crude Oils, their Asphaltene and Related organic Matter Source Inputs from Fula Oilfields
Authors Y. Makeen, W. Abdullah, M. Hakimi, Y. Hadad, K. Mustapha and O. ElhassanThe oils were derived from alga organic matter, which was sourced from sediments deposited in a lacustrine environment under suboxic to relatively anoxic conditions and were generated from mature source rock with a wide range of maturity ranging from early to peak oil window. This is indicated by biomarker compositions based on saturated and aromatic fractions and bulk geochemical characteristics. Previous work by Makeen et al. (2013) on the Abu Gabra shales in the basin shows similar organic matter characteristics, palaeo-depositional environment and maturity, suggesting that the Fula oils are derived from the early Cretaceous Abu Gabra shales. This genetic relationship is also confirmed by the similarities in the structural moieties of the Fula oil asphaltenes and Abu Gabra shale kerogens (Makeen et al., 2015).
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A New Edge-detection Method of Potential Field Based on Discrete Shearlet Transform
More LessIn the potential field explorations, edge detection occupancies the crucial role in the interpretation of geological structure, geological mapping, delineating the mineral range and so on. In this paper, it proposes a new edge-detection method of potential field Based on the combination between Discrete Shearlet Transform theory (DST) and the Mathematical statistics theory. And a combined synthetic model is tested by the proposed method, the experiment presents that the method is very effective in the edge detection with simple algorithm, meanwhile, it shows the more details are retained and the more accurate location is detected with the comparison to three other edge-detection methods.
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Aquatic Oil Spill Remediation by CSASSBs- Cork Sorbent Carrying Automated Sub-Surface Boats
Authors M.D. Imtiaz, A. Aggarwal, J. Chhateja and S. DeiOil spills are environmental catastrophes, which not only lead to major economic losses, but also lead to the destruction of marine ecosystem and loss of aquatic life. These can happen as a result of simple dumping of crude by tankers to spilling of oil in major accidents. The paper briefly discusses the present trend in removal of slick, and puts forward a revolutionary methodology for the same in the form of CSASSB,Cork Sorbent carrying Automated Sub-Surface Boats. The paper is divided into two parts; the first part discusses the effectiveness of the use of CSASSBs, and compares it with the currently used counterparts. The second part discusses the suitability of Cork as the appropriate adsorbing material. The CSASSB has several advantages over the ships that are currently being used, they are more fuel efficient, and also have a larger sorbent bags is to base area ratio. The use of Cork as a sorbent has its own advantages,it is organic and does not cause harm to the environment. The combination of these two revolutionary techniques gives rise to a new comprehensive method for remediation of oil spill sites.
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Prediction with Geostatistics (in free software) of Aluminum Soil Concentrations in a Forest in Southeast of Ecuador
Authors X. Buenanio and G. ChicaizaGeostatistics is a discipline that deals with the statistical analysis of regionalized variables. In this case study, geostatistics is used to determine high values of Aluminum, from a soil sampling done in a forest in the southeast of Ecuador. Free statistical software R and mainly gstat and RGeostats libraries were used. RGeostats is the Geostatistical Package (under R platform) developed by the Geostatistical Team of the Geosciences Research Center of MINES ParisTech. First, exploratory data analysis (EDA) was performed. The second step was the review of a probable presence of drift or trend in the data through the analysis of directional clouds: East and North. Geostatistical tools such as: variogram cloud and variogram surface were used to detect outliers and anisotropy, respectively. An automatic model fitting by Iterative Least Squares was employed to fit the variogram. Finally, Kriging with moving neighborhood was used to get a detailed map of Aluminum soils concentration. The standardized error was reached in the interval [-2.5; +2.5]. The highest values obtained in estimation map belong to the central area. For additional conclusions in relation with toxicity of Aluminum is required to develop a multivariate analysis that includes variables such as pH and average plant growth.
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First Results of 4D Monitoring from the Deepwater BC-10 Life of Field Seismic (LoFS), Brasil
Authors M.A. Galarraga, K. Wang and H.G. FarmerThis paper presents the first results of the time-lapse monitoring from the full field ocean bottom life of field seismic system (LoFS) deployed by Shell at the deepwater BC-10 Argonauta field offshore Brasil, the deepest deployment of this technology in the world. The base survey was completed November 2013, shortly after start of production and the first monitor survey was obtained during June 2014, only 3 months after first water injection. The interpretation of high quality fast-track 4D data volumes identified some key 4D anomalies (softening, hardening, time-shift) that show excellent correlation with the production and injection performance of the field, providing timely input to reservoir management decisions that are essential to enhance and maximize the oil recovery in this field.
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Imaging an Incoherent Wavefield without Cross-correlations - Chaotic Wavefield Gradiometry
Authors S.A.L. de Ridder and B.L. BiondiWe propose a new technique for passive seismic imaging via the direct application of operators to noise recordings. We propose a time-domain 2D scalar wave equation to describe the propagation of surface waves within a narrow frequency range. Outside the source region, this scalar wave equation relates the second-order spatial and second-order temporal derivatives of the wavefield with the local velocity. Different from seismic interferometry, this technique does not rely on cross-correlations to reveal the statistical coherence of a chaotic wavefield at two locations. Rather, it relies on the local measurements of velocity obtained directly from the ratio between temporal and spatial derivatives of the wavefield. The new method allows us to do passive imaging with much shorter passive recording. We apply this technique on ambient seismic recording made at a large and dense array installed over Ekofisk oil field, in the Norwegian North Sea. We are able to image a subsidence-induced geomechanical imprint on the Scholte wave velocities over Ekofisk.
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Improving Repeatability of Land Seismic Data Using Virtual Source Approach Based on Multidimensional Deconvolution
Authors D. Alexandrov, J. van der Neut, A. Bakulin and B. KashtanWe present a new redatuming workflow developed for improving the repeatability of seismic data and designed specifically to account for changes in the source signatures or variations in downgoing fields in general. The new approach is based on the virtual source method with the same potential for reducing non-repeatability, associated with acquisition geometry changes and variations in the near surface. To correct for changes in the source wavelet between surveys, we suggest deconvolving the virtual source gather of the monitor survey with the point-spread function (PSF) of the same survey, and immediately convolving with the PSF of the base or reference survey. The PSF governs the radiation pattern of the virtual source. Trying to completely deconvolve the effects of individual PSFs on each virtual source response may degrade repeatability due to possible amplification of noise. Instead, we try to equalize radiation patterns of the virtual sources across all repeat surveys by reassigning a new reference PSF to all surveys. We apply the deconvolution-convolution method to a field 4D dataset with buried receivers and demonstrate significant improvement in repeatability.
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Quantifying Model Based Uncertainty Using Seismic Uncertainty Analysis – Case Study Danish North Sea
Authors O J Lewis, L. Letki, C. Hidalgo and C. MogensenThis work presents a case study of the application of Seismic Uncertainty Analysis (SUA) in the Danish North Sea where uncertainty in the lateral positioning of faults posed a significant drilling hazard. 500 equivalent models were generated and used to reposition nine key structural objects. Statistical analysis and displays of the repositioned objects were generated to reveal the structural uncertainty and provide quantifiable estimates of the model based uncertainty for use in drilling risk mitigation planning. Structural uncertainty in the pre-stack depth migrated seismic image used for interpretation and well planning is a consequence of the non-uniqueness of the Earth model built by tomography. There are several possible models which will satisfy our data and lead to the same overall gather flatness, but each will result in a different image and different depths of the reflection events. The objective of the Seismic Uncertainty Analysis was to quantify the structural uncertainty of target events in the final seismic image via the derivation of many equivalent TTI Earth models.
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Truncated Gauss-Newton Method with a Modified Scattering-integral Approach for Multi-parameter FWI in Acoustic Media
More LessDensity is difficult to reconstruct in multi-parameter full waveform inversion, due to the cross-talk effects between velocity and density. In this study, we implement the truncated Gauss-Newton method to multi-parameter FWI in acoustic media, in which we incorporate the inverse of the approximate Hessian where the off-diagonal blocks reflect the trade-off effects between different parameters, to decouple the velocity and density during the reconstruction procedure. The model update is computed through the matrix-free conjugate gradient (CG) solution of the Newton linear system. We adopt a modified scattering-integral approach to calculate the gradient of the misfit function with respect to the model parameters and the Hessian-vector product instead of the widely accepted adjoint-state method. The numerical examples prove the feasibility of our method.
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General Optimization Framework for Robust and Regularized 3D FWI
Authors S.R. Becker, L. Horesh, A.Y. Aravkin, E. van den Berg and S. ZhukScarcity of hydrocarbon resources and high exploration risks motivate the development of high fidelity algorithms and computationally viable approaches to exploratory geophysics. Inverse problem formulations for large scale imaging and full waveform inversion have proven very valuable over the past two decades. While initial approaches considered minimizing least squares, recent developments have emphasized the importance of robust formulations, as well as formulations that allow disciplined encoding of prior information into the inverse problem formulation. We propose a generic, flexible optimization framework capable of incorporating a broad range of noise models, forward models, regularizers, and reparametrization transforms. This framework covers seamlessly robust noise models (such as Huber and student’s t), as well as sparse regularizers, projected constraints, and Total Variation regularization. The framework is also expandable - we explain the adjustments that are required for any new formulation to be included. We conclude with few numerical examples demonstrating the versatility of the formulation.
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Use of Low and High Noise Models for Land Surface-seismic Data
Authors W.P. Kimman and P.L. VermeerIn land surface-seismic acquisition ambient noise levels can vary significantly both during a survey and from one survey to another. We show that, for a relatively quiet survey, the addition of increasingly strong realistic noise levels progressively damages the data, especially in the high frequencies. To mitigate such damage, the planned survey effort must offer robustness in the prevailing variable noise conditions. The robustness also renders the data impervious to sensor/system noise in state-of-the-art acquisition systems. In global seismology, Low and High Noise Models are used to describe the range of noise levels encountered on Earth. Models specific to land surface-seismic are not openly available. This may be partly due to the historical use of geophone arrays. High-channel count acquisition systems using broadband digital point-receivers, which have been in operational use in many different areas for more than ten years, provide a new and reliable source of data on acquisition noise levels. From broadband point-receiver ambient noise recordings around the world, we compiled models of the median and extreme values of the noise spectral density. More analysis will be required, but once established, the land surface-seismic noise models can serve as reference for survey and system design.
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Benefits of Blended Acquisition with Dispersed Source Arrays (DSA)
Authors M. Caporal and G. BlacquièreIn blended data acquisition, the recorded wave field is incoherent. Nevertheless blended source units in the arrays are historically chosen to be equal. We propose to abandon this constraint. This allows us to suggest the exploitation of inhomogeneous blended sources, together representing a Dispersed Source Array (DSA). Each source unit involved in the survey might be dedicated to a narrow and arbitrary frequency bandwidth, without the need to satisfy the wideband requirement. Inhomogeneous blending with DSA has several attractive potential advantages. The design of such sources is potentially simpler. In addition, the DSA concept opens the possibility to use tow depths and spatial sampling intervals that are optimum for specific sources. The whole inhomogeneous ensemble of sources incorporated to the array is designed to cover the entire seismic bandwidth of interest.
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Application of High-efficiency Nodal Seismic Acquisition in Niger
Authors Y.L. Huang, W. Wang, M.G. Zhang, X.F. Liang and C.H. WangAs a high-productivity and cost-effective acquisition system, cableless node is widely accepted and deployed in recent years. This paper gives the highlights of some key techniques of cableless node system applied in Niger G&B 3D survey, including multi-fleet vibrators stakeless guidance, high efficiency operation, field QC, and mega data management and processing. We demonstrate that the overall data quality of major geology target and deep formations has been improved through the implementation of the new acquisition in this project, which has proved wide azimuth, high density nodal acquisition is a scientific and cost effective approach in G&B desert area.
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The Role of Interfacial Impedance on Poroelastic Reflection Coefficient
Authors Q. Qi, T.M. Müller and B. GurevichThe characteristics of the seismic P-wave reflection coefficient can depend on the properties of the interface separating two dissimilar poroelastic half-spaces. This interface behavior can be characterized by an interfacial impedance which is associated with various petrophysical scenarios. We study the effects of the interfacial impedance on wave propagation across the interface between gas- and fluid-saturated media as well as a fluid/porous-medium contact. We obtain the reflection coefficient accounting for the interfacial impedance for all frequencies and angles by solving the corresponding boundary value problem. The interfacial impedance shows small influence on the P-wave reflection coefficient for the gas/water contact at seismic frequencies. However, it substantially changes the amplitude and phase angle of the reflected P-wave for a fluid/porous-medium contact.
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Taking Advantage of Hydraulic Fracturing to Improve Gas/condensate Recovery - A Case Study
Authors M. Sheydaeemehr, B. Sedaee sola and A. VataniHydraulic fracturing is one of the most proposed methods to overcome the condensate banking problem around a gas condensate well. This paper investigates the effects of hydraulic fracturing on gas/condensate recovery in one of the world's largest gas condensate fields located in the Middle East. Accumulation of the condensate around a few numbers of wells of this field has resulted in severe deliverability loss. In this study a single compositional well model was constructed and well test data were used to validate the model. The fracture was described as a thin vertical layer positioned symmetrical at the center of the model and the properties of fracture were assigned to this thin layer. A vast number of simulation runs were performed in order to investigate the effects of different parameters on the well production performance. The results showed that hydraulic fracture can significantly improve productivity of this giant field wells and the permeability-width product must be maximized and increasing fracture length would not result in much benefit and the optimum half-length of hydraulic fracture is 125m. Also the effects of negative inertia and positive coupling are dominant in the matrix and the fracture, respectively.
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Micro-CT Pore-scale Analysis of Low Salinity Recovery from Reservoir Sandstones
Authors M. Shabaninejad, R. Marathe, J. Middleton and A. FogdenThe mechanisms of low salinity recovery were investigated by micro-CT imaging of the pore-scale distribution of residual crude oil in clay-rich reservoir carbonates after secondary recovery by high salinity flooding and tertiary recovery by low salinity flooding. A workflow is presented for preparing small mini-plugs (5 mm diameter, 19 mm long) in a holder/flow cell and performing restoration, flooding, imaging and image processing and quantitative analysis. In tomograms of one such sandstone mini-plug after high salinity flooding, the half closest to the inlet was well swept with around 20% residual oil, as disconnected blobs contacting pore walls. The half closest to the outlet had much greater residual due to a substantial capillary end effect, reinforced by the close proximity of the mini-plug walls. Low salinity flooding did not change the oil saturation in the inlet half, while that in the outlet half was greatly reduced by lessening of the end effect. Analysis of interfacial areas in the tomograms showed that oil selectively detached from clay in the inlet half, but remained too disconnected for additional recovery. Oil detached equally from clay and grain in the outlet half, where oil-brine interfacial tension lowering was probably responsible for the artificial extra recovery.
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Forward Stratigraphic Modeling at Appraisal Scale - A Tool to Reduce Facies Uncertainty Distribution in Carbonate Fields
Authors C. Pellan, D. Granjeon, M. Zen and F. BenardCarbonate ramps are usually very good carbonate reservoirs and could be found all around the world, in South-East Asia and Middle-East. Stratigraphic architecture of these reservoirs is a key feature controlling hydrocarbon occurrence and behaviour. Detailed outcrop studies have been performed during the last decade to understand better the structure and facies distribution of carbonate reservoirs, and have led to a considerable improvement of the sequence stratigraphic conceptual models A full stratigraphic parameter set including subsidence map, eustatic curve, production law for the three carbonate sediments, supply of the two clastic sediments, and transport parameters was configured for each sediment. After design of an initial stratigraphic parameter set, a first simulation was performed using DionisosFlow. Once a best-fit simulation was reached, a series of extreme tests was then performed on each stratigraphic parameter to estimate the sensitivity of the numerical simulation, and in particular of the sediment proportions near wells. This stratigraphic forward modelling approach allowed us to understand better the impacts of sedimentary processes on the large-scale carbonate reservoir architecture and thus reduce uncertainties on the appraisal-scale reservoir characterization
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Models and Controls on Sequence Stratigraphy of the Miocene Zhujiang Formation in the Northern Pearl River Mouth Basin
More LessThe Pearl River Mouth Basin is located at the passive continental margin of the northern South China Sea. During the Early Miocene, it was converted from a rifted basin to a down-warped basin and deposited the Zhujiang Formation. Influenced by shelf break migrations, inherited paleo-uplifts, mixing of siliciclastic and carbonate sedimentations, fault breaks and so on, characterizations of sequence stratigraphy of the Zhujiang Fm is different from that of a typical passive margin basin. The study in this paper shows that five third-order sequences in the Zhujiang Fm are recognized and categorized to three types of sequence models. Controls on sequence architectures are characterized by variety and variability in time and space.
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Coquina Carbonate Reservoir Analogues - Key Learnings from the Cretaceous, NE Brazil, and the Holocene, W Australia
Authors P. Corbett, R. Estrella, A. Morales, A. Shoeir, L. Borghi and A.C. TavaresCoquinas are important reservoir units in Pre-Salt reservoirs of the Southern Atlantic. The Cretaceous Morro do Chaves, onshore NE Brazil, has long been considered an analogue for the reservoirs. The Holocene coquina deposits accumulating at the southern end of Shark Bay, Western Australia, have also been proposed as an analogue. In this paper, new petrophysical data from the Cretaceous outcrop have been combined with training images from the Recent analogue to produce geoengineering models for use in reservoir simulation models to understand possible reservoir engineering signatures. In this paper we discuss the learnings that come from these outcrop studies and show how they might be utilised in reservoir characterisation and upscaling studies of coquina reservoirs to improve understanding of reservoir behaviour.
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Coupled Approach Using Stratigraphic Modeling and Seismic Inversion to Enhance Carbonate Reservoir Characterization
Authors C. Pellan, M. Zen, N. Rodriguez Morillas, T. Ait-Ettajer and L. FontanelliA successful exploration well leading to an economically valuable discovery, kick off new challenges for the Appraisal phase and future development of the field, especially in carbonate environment where spatial continuity of facies can be limited. A phase of detailed reservoir characterization is starting, where bringing tools and concepts from exploration at lower scale and higher resolution can add value to classical methods. In this framework, results of 4D Forward Stratigraphic Modeling combined with Seismic Inversion can be a useful tool to assess spatial boundaries of facies, and thus optimize well number and location on a reliable basis. The high resolution reached by stratigraphic modeling in low transport carbonate environment is bringing added value to the coarser resolution of seismic interpretation, and Acoustic Inversion. It is also integrating the very high resolution but spatially irrelevant well information. Thus, a high level of detail regarding the reservoir composition is reached, taking into account sequence stratigraphy principles. Furthermore the common and coherent features observed by two radically different approaches (Inversion form seismic data, and forward stratigraphic modeling) are strengthening the reliability of both techniques.
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Combined Rock-Physical Modelling and Seismic Inversion Techniques for Characterisation of Stacked Sandstone Reservoir
Authors A. Justiniano, M. Jaya, G. Diephuis, R. Veenhof and T. PringleThe objective of the study is to characterise the Triassic massive stacked sandstone deposits of the Main Buntsandstein Subgroup at Block Q16 located in the West Netherlands Basin. The characterisation was carried out through combining rock-physics modelling and seismic inversion techniques. The application of inversion on time-converted PSDM stack results in better seismic impedance resolution due to better well-seismic match performance. The results show that even though the Bunter reservoir consists of lithologically uniform massive stacked sandstones, the obtained rock property volumes allow distinguishing two zones within the target unit. The upper zone - Hardegsen and Detfurth Formations - exhibits on average lower acoustic impedance, shear impedance and bulk density values compared to the lower zone - the Volpriehausen Formation. These differences are essentially attributed to changes in porosity. Larger porosities make these rock properties decrease. Moreover, it is believed that locally the entire Bunter reservoir is gas-bearing, but the Volpriehausen sandstones are tighter. Vp/Vs ratio and Poisson’s ratio are good gas-fluid indicators. Both decrease for Bunter reservoirs compared to shales of the Solling and Rogenstein Formations. Furthermore, the rock property volumes allowed improved mapping of top and base of the Bunter reservoir compared to the original seismic reflectivity volume.
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Closed-Loop SRME with Data-reconstruction
Authors G.A. Lopez Angarita and D.J. VerschuurTo obtain an accurate surface multiple estimation via data-driven methods, dense source and receiver sampling is required. The traditional approach to this problem consists in performing data interpolation prior to multiple estimation. Though appropriate in many cases, this methodology fails when big data gaps are present or when relevant information (e.g. near-offset data in shallow-layer environments) is not recovered. We propose a solution in which multiple estimation is performed simultaneously with data reconstruction. For this purpose we propose to extend the recently introduced Closed-Loop SRME (CL-SRME) algorithm to account for the primary estimation in the case of coarsely sampled data. This is achieved by introducing a focal domain parameterization in a sparsity-promoting CL-SRME method. This algorithm will show its capacity to reconstruct large data gaps and provide reliable primary estimations, even in the presence of large under-sampling and missing near offsets.
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Finite Difference Modelling with (2M)Th-order Spatial and (2N)Th-order Temporal Accuracies for 2D Acoustic Wave Equation
More LessWe develop the method introduced by Liu et al. from (2M)th-order accuracy both in space and time domain to (2M)th-order accuracy in space and (2N)th-order accuracy in time, by which we can save a lot of computational cost without decreasing the accuracy. The dispersion and stability analysis show that the new stencil with (2N)th-order temporal accuracy can obtain smaller dispersion, greater accuracy and better stability than the conventional stencil. Increasing the number of points off the axial in the new stencil can further increase the temporal accuracy but this also increases the computational cost. By utilizing the new stencil, a larger time sampling interval can be used while maintaining the accuracy. Therefore some N and some time sampling interval can be used to achieve the smallest computational cost while maintaining the accuracy. Modelling examples demonstrate the advantage of the new stencil over the conventional stencil.
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Converted Wave RTM Using Lowrank Wavefield Extrapolation
Authors L. Casasanta, Z. Xue and S.H. GrayAlthough wavefield extrapolation techniques are well developed for P-wave seismic imaging, ray based migration algorithms are still the workhorse for converted-wave (PS-wave) depth imaging. Full (exact) elastic-wave reverse-time anisotropic migration (RTM) has not been widely adopted for reasons of computational and workflow efficiency, despite its potential to deliver accurate sub-surface images in complex geological settings by directly solving the elastic wave equation. Even (approximate) converted-wave RTM in anisotropic media, using separate finite-difference propagators for quasi-P and quasi-S waves, is limited in applicability for algorithmic reasons. Here, we introduce an alternative converted-wave anisotropic RTM, using a low-rank decomposition of mixed-domain space-wavenumber propagators for quasi-P and quasi-S waves. These operators are formal integral solutions of the pure-mode wave equations which guarantee stable and dispersion-free time extrapolation for coarse time steps in anisotropic, heterogeneous media. The pure-mode extrapolators are attractive for both PS-wave structural imaging and velocity analysis. An ocean bottom cable synthetic example illustrates the effectiveness of low-rank PS-wave RTM when compared against state-of-the-art Gaussian beam and finite difference RTM algorithms.
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Curvelet-based 3D Reconstruction of Digital Cores Using POCS Method
More LessWith the development of shale-gas exploration and exploitation, it is necessary to study the 3D spatial distribution of shale fractures for research on shale rock physics. Because of limitations of instruments, accurate shale slice is discontinuous in depth, and the minimum interval between adjacent slices in depth is inconsistent with horizontal resolution of digital cores. Those are the main factors which can prevent accuracy improvement for fracture characterization and physical modeling of digital cores. In order to study the 3D spatial distribution of fractures, this abstract achieves reconstruction of 3D digital cores using Project Onto Convex Sets (POCS) method in curvelet domain. Tests on sand dataset obtained from X ray scanner and accurate shale rocks obtained by focused ion beam scanning electron microscopy (FIB-SEM) demonstrate the validity and superiority of the proposed method.
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Brittleness Index Research Based on the Anisotropic Seismic Rock Physics for Tight-oil Sandstone
Authors X.R. Huang, J.P. Huang, Z.C. Li, Z. Guan and Y. YangCurrent seismic rock physics model for tight sandstone is not sufficient to depict its complicated microstructure. In this paper, we build a seismic rock physics model from five aspects which are clay type, filler content, pore connectivity, pore type and vertical fracture. The new Brittleness index is established based on the new rock physical model. In order to detect the superiority of the new Brittleness index in brittleness prediction, we compare it with other conventional Brittleness indexes in aspects of brittleness sensitivity and physical response. The results show that the ability to characterize the mineral’s brittleness of new brittleness indexes is much stronger than the ability of conventional brittleness indexes. And the analysis about cross-plot colour-coded by the new Brittleness index could support the favoriable informations for elastic property and brittle characteristics in “sweet spot” zone of tight sandstone oil reservoir. In theory, the above characteristics of new brittleness index are more conductive to brittleness evaluation for tight sandstone oil reservoir.
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Crustal Structure of the Galicia Continental Margin (NW Spain) from Gravity Data Analysis and Modelling
Authors M. Druet, A. Muñoz-Martín and A. CarbóBetween 2001 and 2008, new marine gravity data have been collected over the North Atlantic Ocean rounding Galicia margin (NW Spain). We present a gravity data analysis and a N-S density model, focused on the interpretation of the crustal structure of the margin. For that purpose, a Complete Bouguer Anomaly grid has been calculated. This grid has been filtered in the frequency domain (both low-pass and band-pass filtering) to generate, respectively, a long-wavelength Bouguer Anomaly map (related to lithospheric mantle sources) and a mid-wavelength Bouguer Anomaly map (related to crustal density variations). Additionally, a N-S density model across this area has been performed. The analysis of these new data reveals the presence of compressive tectonics on this margin, particularly to the North, that generates crustal shortening and uplift of the seamounts area. During the Cenozoic compressive stage, besides the inversion of previous normal and strike-slip faults, new compressive structures are generated in the northern edge of the seamounts area, leading to the thickening of oceanic crust by means of a crustal-scale great fold and thrust, which is the westward continuation of those structures observed on the North Iberia compressive margin.
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3D Envelope Inversion
More LessThe envelope of the wavefields carries ultra low frequency information which can be used to recover the large-scale component of the model, and the initial model dependence of full waveform inversion can be reduced. We extended the envelope inversion method to 3D and used GPU clusters for the implementation, Numerical tests using the resampled 3D Overthrust model proved the validity and feasibility of the proposed approach. The inverted velocity from the combined (EI+WI) envelope inversion plus waveform inversion indicated that it can deliver much improved result compared with regular full waveform inversion.
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Laplace-domain Waveform Inversion for the 3D Acoustic-elastic Coupled Media
More LessIn the marine streamer survey, the sources and receivers are located in the homogeneous acoustic media; however, the media below the sea bottom, which is the target area, has highly heterogeneous 3D elastic properties. Thus, the hydrophone pressure data contain various elastic effects, such as shear wave effects, mode converted waves and amplitude offset variation, and these effects impact the Laplace-transformed wavefield. Therefore, it is not possible to perfectly reduce the misfit between modelled and observed data using only acoustic wave equations. In this study, we developed a Laplace-domain waveform inversion algorithm for 3D acoustic-elastic coupled media. We can precisely simulate the environment of a conventional streamer marine survey by coupling the 3D acoustic and elastic wave equations using a proper boundary condition at the solid-fluid interface. Also, for the matrix solver, we suggest using the parallel sparse direct solver library, which was developed by the MUltifrontal Massively Parallel Solver (MUMPS) team. Because this is a direct matrix solver, we do net lose the main advantage of implicit modeling (e.g., frequency or Laplace domain modeling) over the explicit time-domain modelling when we solve the wave field for a number of shots.
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Seismic Imaging of Two-layer Deformation Lithosphere in the Indian Ocean
More LessWe obtain a very deep seismic image from the offshore northern Sumatra that shows faults down to 45 km depth by boosting low frequency signal during data processing, which is much better than the traditional processed result. The amplitude of these deep reflectors in the mantle decreases linearly with depth down to 25 km and then remains constant down to 45 km. We also find that the number of faults, the number of earthquakes and the cumulative moment released as a function of depth show a similar pattern, suggesting that the lithospheric mantle deformation in this region can be divided into two layers: a highly fractured serpentinized upper layer and a pristine brittle lithospheric mantle where great earthquakes initiate and large stress drop occurs. It is also consistent with the depth of second layer of double Benioff zone in most of the subduction zones.
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Plane-wave Least-square Reverse Time Migration with Source Polarity Encoding
Authors C. Li, J.P. Huang, Z.C. Li, R.R. Wang and M. YuanPlane-wave least-square reverse time migration (PLSRTM) delivers high quality images but costs less computation compared with conventional least-square reverse time migration. However, a number of plane-waves are necessary for crosstalk suppression. The paper introduces source polarity encoding to the plane-waves to reach better suppression to crosstalk. Combined with randomized sampling approach, the computation cost of PLSRTM can be decreased a lot. Numerical tests on SEG rugged topography model verifies that the combination with source polarity encoding and randomized sampling can obviously improve the imaging result and computation cost of PLSRTM.
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A New Approach to Reservoir Modeling and Simulation Using Boundary Representation, Adaptive Unstructured Meshes and the Discontinuous Overlapping Control Volume Finite Element Method
Authors P. Salinas, J.R. Percival, D. Pavlidis, Z. Xie, J. Gomes, C.C. Pain and M.D. JacksonWe present a new, high-order, control-volume-finite-element (CVFE) method with discontinuous Nth-order representation for pressure and (N+1)th-order for velocity. The method conserves mass and ensures that the extended Darcy equations for multi-phase flow are exactly enforced, but does not require the use of control volumes (CVs) that span domain boundaries. We demonstrate that the approach, amongst other features, accurately preserves sharp saturation changes associated with high aspect ratio geologic features such as fractures and mudstones, allowing efficient simulation of flow in highly heterogeneous models. Moreover, in conjunction with dynamic mesh optimization, in which the mesh adapts in space and time to key solution fields such as pressure, velocity or saturation whilst honoring a surface-based representation of the underlying geologic heterogeneity, accurate solutions are obtained at significantly lower computational cost than an equivalent fine, fixed mesh and conventional CVFE methods. The work presented is significant for two reasons. First, it resolves a long- standing problem associated with the use of classical CVFE methods to model flow in highly heterogeneous porous media; second, it reduces computational cost/increases solution accuracy through the use of dynamic mesh optimization without compromising parallelization.
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3D Modeling of the CoalBed Methane (CBM) Resources in the Taldykuduk Block Karaganda Coal Basin, Kazakhstan
Authors J.J. Royer, R. Sadykov, I. Panfilova and E.K. OgayCoal Bed Methane (CBM) is gas stored in coal layers, generally extracted from wells after hydraulic fracturing and/or CO2 or solvent injections. The Karaganda Basin was selected to develop CBM production because of its huge gas potential (4 300 Bm3 equivalent to 2 billion tons of coal, with gas content about 15-25 m3/t of coal (for comparison San Juan basin, US, has < 20 m3/t)). This work aims at modeling the Taldykuduk block coal layers focusing on CBM production. The methane extracted during mining actually released in the atmosphere, will be collected. A 3D geological model was built on Gocad/Skua using all available datasets (about 1000 wells over 84 km2, cross-section and maps acquired during coal exploitation, and fractures network reported on geological cross sections). The resulting 3D model including hundreds of faults, is used to simulate the secondary recovery of methane by CO2 injection on a flow simulator, assuming a two phase dimensionless formulation in a double porosity model with the matrix (m) and the fracture (f) for which the initial and boundary conditions are different. The resulting 3D models had helped in better understanding the regional tectonic structures, faults relationships, the hydrogeology regime and the potential gas reserves.
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Performance of Water Injection Wells - Chestnut Field
Authors M. Langford and J. TovarWater injectors are critical to the long-term success and reserves recovery of hydrocarbons production and reservoir management. Injectors are also critical to the pressure support of the reservoir that allows production and mechanical integrity of the rock. Lack of injection does, in many cases, lead to impaired production and changes in petro-physical properties at the wellbore and deep into the reservoir. Limited references are found in the literature in terms of design and performance management of water injectors. Our work describes in detail the design and performance processes for two (2) injection wells (wells 12 & 17) in the Chestnut field, located in block 22/2a in the UKCS of the North Sea. Producing from a shallow sandstone reservoir, the field is exploited using two (2) producers and two (2) injectors. All wells are subsea and an active sand and pore pressure management program has been in place for 6 years. The design rationale and parameters are presented and the results obtained discussed. Well performance is then analysed in terms of pressure support, injectivity and operational problems that lead to injectivity impairment and one well failure. The methodology for evaluation of reservoir performance is described; comparison between the typical analytical tools such as the Hall or the Impedance Methods is discussed including the results obtained. A performance comparison based on real-time data from the wells, to identify and predict events such as injectivity impairment, the need for intervention or remedial action, is presented.
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An Alternative Hydrocarbon Indicator Based on Rock Physics Template
More LessReservoir fluid discrimination is an indispensable part of seismic exploration. Reliable fluid discrimination helps to decrease the risk of exploration and increase the success rate of drilling. Based on the H-M contact theory, a rock physics template was built in the domain of the crossplot of compressional modulus and ratio of compressional modulus and shear modulus. An alternative hydrocarbon indicator RPTI (rock physics template indicator) was proposed according the fluid trend in this rock physics template. This combined hydrocarbon indicator not only solves the problem easily caused by single indicator in discrimination, but also reduces the influences of human factors. A corresponding alternative elastic impedance inversion method was proposed based on the Bayesian theory to improve the accuracy of inversion results. The profile of this indicator is an intuitionistic interpretation of fluid contents. Real data tests demonstrate the applicability and validity.
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Ray-tracing-based Input Data Selection RTM - A Target Oriented Approach for Clearer Subsalt Image
Authors C. Peng Inc, W. Gou Inc and G. Liu Inc IncWe present an input data-selection workflow based on 3D ray-tracing to improve the reverse time migration image in areas of poor illumination and low signal-to-noise ratio. It is effective for imaging subsalt three-way closure with weak subsalt primaries and strong noise levels. The workflow can be applied to any type of survey, but it is most suitable for full azimuth geometries. We focused on data selection using 3D ray-tracing, but this workflow can be easily adapted to use finite-difference wave-equation modelling. The data selection information can either be used to scale up weak primary signal before migration or to be migrated separately and merged into a full migration result in the post-migration stage.
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Accurate Seismic Wavefield Simulation in 3D Heterogeneous Media - A Massively Parallel Algorithm
Authors M.K. Sen, P.L. Stoffa and R. Seifty, anisotropy, viscosity and poro-elasticity are now becoming increasingly more important for analysis of multi-azimuth and rich azimuth data. Here we present an algorithm for solving anisotropic wave equation in 3D in which spatial derivatives are computed in Fourier domain while time updates are computed using the rapid expansion method. Although the use of the pseudo-spectral method together with REM ensures a desired level of accuracy, the algorithm is memory and CPU intensive. To address this, we have developed several parallelization strategies – one such approach involves computing wavefields in different parallel banks and uses parallel FFTs ensuring minimal communication overhead. The algorithm can handle arbitrary anisotropy including monoclinic media. We will present several examples for models with varying degree of complexity and anisotropy. The algorithm can easily be extended to perform reverse time migration in elastic media.
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Differential Kuster-Toksöz Rock Physics Model for Multiple-porosity Rocks
More LessKuster-Toksöz model (KTM) is a classical rock physics model concerning the influence of pore geometry on elastic wave velocities. However, this model is limited to dilute concentration of pores. That is to say, the porosity could not be too high (porosity (Φ)/aspect ratio (α) <<1). In order to solve this problem, this paper transforms the Kuster-Toksöz model into a differential Kuster-Toksöz treatment. In other words, we consider a process whereby porosity, or equivalently inclusions with certain geometries, increases step by step from zero up to its final value. Obviously, this new differential Kuster-Toksöz model (DKTM) is superior to the classical KTM and DEM (short for differential effective medium) model since it considers multiple–porosity and higher porosity rocks. Furthermore, when void pores and clay are considered as inclusions, we analyze the elastic moduli simulated by KTM and DKTM, the geometry parameter of which is described by Berryman’s special pores. The result shows that, DKTM is superior to KTM for obtaining satisfactory elastic properties under high porosity and high volume fraction inclusion condition.
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3D Facies Model in Large-scale Fan Delta Complexes (Montserrat and Sant Llorenç del Munt, Eocene, Ebro Basin, NE Spain)
Authors M. Diviu, P. Cabello and M. López-BlancoAn exploration scale facies model (375 km2 and 325 m thick) of two outcropping fan-delta complexes developed during the Eocene in the SE Ebro basin margin was produced. Input data for the model comprises detailed geological maps. This model satisfactorily captures the heterogeneity linked to the T-R cyclicity at two scales. The transgressive and regressive organization of coastal facies belts (at scale of sequence sets and composite sequences) was achieved by the reconstruction of key surfaces and modelling facies belt boundaries in between by using the linear expectation trend of TTG algorithm. The position of these facies boundaries was fixed on the basis of paleogeographic maps extracted from detailed field mapping. Due to its small scale expression, high frequency cyclicity (fundamental sequences) was addressed by the stochastic part of the TTG algorithm. The model reproduces a continuous delta front facies belt connected along the different sequences. However, its complex geometry also capture the existence of potential stratigraphic traps related to the endings of fan-delta front reservoir analogue facies wedges into prodelta and distal alluvial mudstones resulting from the T-R cycles at composite sequence scale.
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Deciphering Turbidite Triggers by Core Facies Analyses. Implications for Geohazards and Reservoir Characterization
Authors J.P. Corella, B.L. Valero Garcés and J. GerardSediment cores retrieved in turbidite sediments from modern lacustrine systems enable to understand the sedimentological processes and depositional patterns of turbiditic flows as well as to evaluate their triggering mechanisms. Lacustrine turbidites were analysed in Lake Montcortès situated in NE Iberian Peninsula (42º 19´N / 0º 59´E). Multiproxy core facies analyses were applied to investigate the turbidite record of this karstic lake system. Integration of geochemical, geophysical and sedimentological analyses and micro-computed tomography (micro-CT) imaging led to the identification of two types of turbidites and distinct triggers have been proposed to generate them: i) low density turbidity currents resulting from sediment-laden hyperpycnal currents related to extreme floods in the watershed and ii) seismic-induced subaquatic slope failures. Geohazard assesments can be implemented by understanding the variability of these extreme events (earthquakes, tsunamis and large floods) preserved in the sedimentary record at centennial to millennial scales. In addition, deciphering triggering mechanims in core facies analyses may have significant economic implications as both processes eventually lead to different turbidites geometries and textures that may affect reservoir quality although lacustrine turbidites are not the most common hydrocarbon reservoirs.
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Least-Squares Reverse-Time Migration of Simultaneous-Source Data
Authors W. Dai, W. Lewis and R.T. CoatesSimultaneous-source recording, where multiple shots are fired at very similar times and recorded by the same receiver array, has been proposed as a method of both improving source sampling and reducing survey acquisition costs. However, this acquisition method complicates the subsequent processing considerably, requiring either data separation or an imaging method capable of accepting simultaneous-source data as input without generating artefacts or crosstalk. In this paper we demonstrate that least-squares reverse-time migration (LSRTM) is a promising candidate algorithm for this application. Using the 3D SEG Advanced Modeling Program (SEAM) salt model we show that LSRTM can effectively image simultaneous-source data suppressing crosstalk while at the same time improving bandwidth.
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Simultaneous Shooting for Sparse OBN 4D Surveys and Deblending Using Modified Radon Operators
Authors R.R. Haacke, G. Hampson and B. GolebiowskiSignificant gains in productivity (and savings on survey time and cost) have recently been achieved using simultaneous sources with high-density Ocean Bottom Cable geometries. However, where the acquisition is receiver-bound, using sparse Ocean Bottom Node (OBN) arrays for example, the argument for use of simultaneous sources is less compelling. Time and motion analysis for a rolling array of sparse OBN, spaced by 390 m with a 30x30 m shot carpet, shows that time savings of the order of 10 % of the equivalent single-source survey duration should be expected. Although small this may be significant in tightly constrained acquisition seasons. Since time-lapse surveying is the main motivation for many sparse OBN acquisitions, the saving in survey time must be balanced against the risk of additional 4D noise created by simultaneous-source crosstalk. Attenuating crosstalk using a new form of Radon operator implemented with cascaded fx prediction and interpolation as part of a kill-fill process, the level of 4D noise created by simultaneous sources is reduced to an ambient level of 6 %, with a highly randomized character, after imaging.
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Free-surface Multiples and Full-waveform Inversion Spectral Resolution
Authors V.V. Kazei, B.M. Kashtan, V.N. Troyan and W.A. MulderLow frequencies play a crucial role in the convergence of full-waveform inversion to the correct model in most of its current implementations. However, the lower the frequencies, the bigger are the amplitudes of the surface waves, causing the inversion to be driven by the latter. If they are not blanked out or removed, this may lead to convergence problems. To analyze this situation, we consider the simplest case where surface waves are present: an acoustic layer over a halfspace. We earlier analyzed the contributions of various wave types to the wavenumber spectrum of a velocity perturbation above a reflecting halfspace, without a free surface. Here, we extend this spectral sensitivity analysis to the case with a free surface, which generates multiples and ghosts. In this setting, the surface guided P-waves can be considered as a superposition of free-surface multiples. Our analysis shows that the conditioning of the linearized inverse problem, which is solved at each iteration of full-waveform inversion, becomes worse when multiples are taken into account. At the same time the inclusion of multiples increases the sensitivity to some low wavenumbers in the model spectrum, which should be beneficial for full-waveform inversion once a suitable preconditioner has been found.
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Well Constraints in Full Waveform Inversion and its Application in Time-lapse Seismic
More LessFull waveform inversion (FWI) has become an integral part of the velocity model building flow due to its resolution, especially in the shallow regimes. Most of the times the wide angle acquisition is not available because of its expense and we still would like to use the power of FWI by utilizing the vintage data. In these older prospects since there is a lot more geological information available besides just seismic data, we can use information from wells for example, to constrain the FWI iterations. Even though well information is at our disposal it is difficult to incorporate it into the traditional FWI which is represented by data misfit objective function. We incorporate wells in the model is to build an apriori model from them and take this into account in the objective function. The objective function can be extended by a model misfit term alongside the data misfit one. We demonstrate how the new objective function works on real data. Furthermore we introduce two workflows to recover model difference between the base-line and the monitor or monitor surveys by FWI in the time-lapse seismic world.
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Elastic Waveform Inversion with Modified Surface Boundary Conditions for Land Seismic Data
Authors C.A. Pérez Solano and R.E. PlessixWe present an elastic waveform inversion for low-frequency wide-aperture land seismic data. The presence of wavelength-sized contrasted layers limits the applicability of acoustic inversion. This happens above about 3 Hz when a few hundred meters thick carbonate layers interleave with shale/sand layers, as seen in the Middle East. Elastic inversion is challenging because of computational cost and, in land, because of ground roll. To retrieve the long-to-intermediate wavelengths of the P-velocity, we invert the weak diving waves and remove ground roll in the pre-processed data. We modify the surface boundary conditions and obtain an elastic modelling without surface waves by zeroing the normal derivatives of the shear stresses at the surface. An analysis of this modification shows that the reflection coefficients become independent of the velocity ratio and the PP-reflection coefficient is similar to the acoustic one. This modification allows us to develop approximate elastic modelling of diving/transmitted waves without implementing ground-roll suppression for the modelled data. Moreover, it allows us to use large velocity ratios to speed-up the inversion without degrading the resulting P-velocity model. This approach can be seen as intermediate between acoustic and elastic inversion with free-surface conditions. We illustrate it with synthetic and real data examples.
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VSP Measurements Used as a Tool for Sub Salt Near Field Development
Authors T. Bartels, M. Gelhaus and M. HumphriesMany of the Rotliegend low permeability dry gas fields in the Southern Permian Basin in northern Germany are covered by salt dome structures that lead to imaging problems in subsalt reservoir between 4000 m to 5000 m depth. As compartmentalization is the key challenge in field development high resolution seismic is essential for well planning. Only a vintage 3D seismic from 1993/94 with limited quality exists. Acquisition of new 3D seismic is not possible due to permitting restrictions and public resistance. Therefore the focus is on the acquisition of 2D VSPs in every new drilled well. The VSP measurements give local insights. With a general structural understanding and production history in mind those local insights can be merged into the overall picture and generate immense value for the understanding of the field.
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Incorporating Seismic Velocity Data in AVO/AVA Low Frequency Models by Honoring Local Geology
More LessLow frequency information is required for quantitative reservoir characterization. Because borehole measurements are laterally sparse and preferential towards reservoir locations, there is much uncertainty on the low frequency models away from well control. Methods to improve the reliability of the low frequency data include the use of low frequency update schemes or seismic attribute maps. The use of seismic velocity data for trend modeling is well recognized, but the methodology for incorporating the velocity is not always clearly described. Especially in case of an AVO/AVA study, where low frequency information for several elastic properties is required, a rigorous workflow is desired. Here, we propose a method to include seismic velocity data. The methodology uses local geological knowledge through rock physics relations. We validate the method by comparing results of a more common method with our proposed workflow at blind wells. This shows that a low frequency model that does not use the velocity data misses significant lateral variations that are representative of the local geology.
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Velocity-porosity Evolution of Mechanically Compacted Brine-saturated Sand-clay Mixtures
Authors M. Koochak Zadeh, N.H. Mondol and J. JahrenIn this study, four brine-saturated specimens of unconsolidated sands and sand-clay mixtures are tested to infer velocity-porosity trends of sand-dominated facies when a full control on mineralogy is applied on the tested samples. The current results show consistency with the published experimentally derived compaction trends of natural sands. The iso-stress curves connecting the data points with the same effective stress in the velocity-porosity plot are comparable to the friable sand model curves proposed to estimate the rock properties of sands within the mechanical compaction domain. As expected, the achieved iso-stress curves for mechanically compacted samples are too far away from the empirical lines suggested estimating rock properties of sandstones within the chemical compaction domain. To check creditability of the rock physics models in both mechanical and chemical compaction domains, the log-derived petrophysical properties acquired from the North Sea are compared to the derived experimental compaction trends. The shallow unconsolidated sands follow closely the experimentally derived iso-stress curves and friable sand model but, the consolidated sandstones show a wide range of physical properties and may sometimes follow different trends compared to suggested rock physics models.
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